Cathode ray picture scanner



A ril 2, 1940.

R. URTEL CATHODE-RAY PICTURE SCANNER Filed June 8, 1937 rmwmrme msA/csaw/m was [Afar/2005 70 AMPl/F/FR & TRAMSM/TTER DFFLECI/ON CONTROL'INVEFNTIOR RUDOLF 0pm ATTORNEY Patented Apr. 2, 1940 UNITED sTATEs2,196,130 OATHODE RAY norms some Rudolf Urtel, Berlin, Germany, assignorto Telefunken Gesellschaft fiir Drahtlose Telegraphic m. b. H., Berlin,Germany, a corporation of Germany Application June 8, 1937, Serial No.146,990

In Germany June 9, 1936 12 Claims.

This invention relates to cathode ray picture scanners and inparticular, to method and means for compensating for disturbances insuch tubes which result in irregular brightness distribution at thereproducer of the receiver.

In cathode ray picture scanners, even when the picture to be transmittedconsists of a surface with uniform brightness and without any details,there can be noted an irregular distribution of the brightness at thereceiver side, such as shown for instance in Fig. 1. This distributionof the brilliancy designated in the following as disturbance signal,occurs at the transmission of a tele-picture and is observed asadditional blackening of the receiving image. It is possible tocompensate this disturbance signal in that a compensation signal isproduced artificially at the transmitter side which when added to, orsubtracted from the output currents of the cathode ray scanner,causes'at the receiver side just the disappearance of the saiddisturbance signal as shown, for example, in my copending applicationSerial No. 107,815, filed October 27, 1936, and entitled Signallingcircuit. But the value of the disturbance signal is dependent on theoperating conditions of thecathode ray scanner, such as for instance onthe average brightness of the image to be transmitted into distance. Itfollows therefrom that during the telecast it is not possible: to usealways the same compensation signal, but the apparatus furnishing thecompensation signal must be subsequently adjusted with regard to thevariations of the mean brightness, if importance is to be attached to analways exact compensation.

In order to avoid this disadvantage, in addition to the light forprojecting the image, a diffuse beam of light rays having the same lumnous density throughout its entire section 40 impinges on thephotosensitive surface of they scanner in accordance with the invention.At this additional diffuse irradiation the fluctuations of the totallight current impinging on the scanner, are proportionately lower thanwithout the said diffuse light. Consequently, the variation in the valueof the disturbance signal is likewise smaller than if the time Variationof the preliminary light impinging on the scanner has its cause solelyin the variations of the average brightness. The slight residualvariations in the value of the disturbance signal can fr thermore beeliminated if the diffuse preliminary light is continuously varied infunction ofthe average brightness, such that the total light currentimpinging on the cathode ray scanner remains constant as to time. Inthis case the effect of the average brightness upon the disturbancesignal is entirely obviated, and hence, during the entire telecast thesame setting of the apparatus furnishing the compensation signal can beused without the disturbance signal ap pearing at the receiver side.

The invention will now be described in detail with reference to thedrawing in which:

Fig. 1 shows diagrammatically the non-uniform distribution ofillumination at the receiver due to dark-spot disturbances at thescanner;

Fig. 2 shows diagrammatically one embodiment of the invention in whichdiffused light of constant intensity is superimposed on the imageillumination on the mosaic electrode;

Fig. 3 shows a modification of the embodiment shown in Fig. 2 whereinthe intensity of 1 the diffused light is controlled by the average valueof the imageillumination while;

Fig. 4 shows a modification of the embodiment shown in Figs. '2 and 3wherein a different method and means of projecting the diffusedillumination is provided.

In Fig. 2, item Ill represents the object to be telecast, II is anobjective projecting an image of the object on a transparent screensurface l2, and I3 is a cathode ray scanner on whose photosensitivesurface M the projection screen I2 is reproduced by means of a furtherobjective IS. The entire projection surface It is illuminated by diffuselight across a dispersion lens I! which light is furnished by the sourcel6 having constant brightness.

The photosensitive surface M of the scanner therefore is impinged by aluminous current composed of a constant component supplied by the lampl6, and a varying component corresponding to the average brightness ofthe image of the object ID. The proportionate variations of the entireluminous current obviously are smaller than those of the average imagebrightness, and therefore, the variations of the disturbance signal arelikewise smaller at unchanged setting of the appartus furnishing thecompensation signal, than in the hitherto customary operating mode inwhich the light source 16 was absent.

Fig. 3 shows a mode of construction in which the object It is reproducedby means of the objective l5, directly on the photosensitive surface I4of the scanner I3. Between the objective l5 and the scanner iii, areflecting arrangement, for instance an oblique glass plate H3 isinserted which may eventually be adapted. as a semipermeable mirror.Between the plate It and the lamp l6 again the dispersion lens H isprovided The lamp i8 is connected to an amplifier l9 controlled by thephotocell 26 which as such determines the average image brightness.

The arrangement according to 3 operates l5, increases at first.

also the current furnished by the photocell 20 and conducted to theamplifier l9 increases. This amplifier is so adapted that its outputcurrent and hence, the brightness of the lamp [6 become smaller so thatless light arrives from the lamp l6 at the scanner across the reflectingdevice l8, than at a lower average image brightness. The characteristicof the amplifier I9 is now so set that the total luminous currentimpinging on the surface I always remains at least approximatelyconstant.

In Fig. 4 another mode of construction is shown inasmuch as it differsfrom that according to Fig. 3. The glass plate l8 of Fig. 3 is replacedby a smaller mirror 2| covering up a small portion of the stuface of theobjective [5, and projecting the light of the tube It upon the totalphotosensitive surface 14 of the scanner.

The invention can be equally well applied to the transmission of openair scenes or stage scenes as well as for the transmission of films, andin the latter case the application is especially simple when the filmsare projected by means of a projector equipped with optical com--pensation means.

What I claim is:

1. In a television system wherein is provided a cathode ray scannerequipped with a mosaic electrode, the method of improving the operationwhich comprises the steps of projecting light images of objects ofvarying light intensity to be transmitted upon the mosaic electrode, andsimultaneously illuminating the mosaic electrode by a flooding lightbeam of substantially uniform density over the entire mosaic area and ofan intensity which varies inversely with increases in average brilliancyin the light image for maintaining the total illumination upon themosaic at a predetermined substantially constant value.

2. In a television system wherein is provided a cathode ray tube scannerequipped with a mosaic electrode, the method of improving the operationwhich comprises the steps of projecting a light image of an object uponthe mosaic electrode, and simultaneously irradiating by a flooding lightbeam the entire mosaic area with diffused light having constant densityof illumination.

3. In a television system wherein is provided a cathode ray tube scannerequipped with a mosaic electrode, the method of improving the operationwhich comprises the steps of projecting a light image of an object uponthe mosaic electrode, and simultaneously superimposing by a floodinglight beam upon the entire mosaic electrode area light of constantintensity and constant density.

4. In a television system wherein is provided a cathode ray tube scannerequipped with a mosaic electrode, the method of improving the operationwhich comprises the steps of projecting a light image of an object uponthe mosaic electrode, simultaneously superimposing by a flooding lightbeam upon the entire mosaic electrode area light of constant intensityand constant density, and regulating the intensity of the flooding lightbeam in accordance with the average value of illumination of the lightimage.

5 In a television system wherein is provided a cathode ray tube scannerequipped with a mosaic electrode, the method of improving the operationwhich comprises the steps of projectinga light image of an object uponthe mosaic electrode, simultaneously superimposing by a flooding lightbeam upon the entire mosaic electrode area light of constant intensityand constant density, and regulating the intensity of the flooding lightbeam inversely proportional to the average light value of illuminationof the light image.

6. In a television system wherein is provided a cathode ray scannerequipped with a mosaic electrode, the method of improving the operationwhich comprises the steps of projecting a light image of an object uponthe mosaic electrode, simultaneously superimposing by a flooding lightbeam upon the entire mosaic area diffused light of constant density,scanning the mosaic to produce distorted signals representative of theillumination of the combined image and diiiused light, and transmittingthe produced signals together with signals for compensating for thedistortion.

7. A television system comprising a cathode ray tube having a mosaicelectrode, means for projecting light images of objects of varying lightintensity to be transmitted upon the mosaic electrode, and optical meansincluding a flooding light beam of uniform density projected over theentire mosaic electrode area for simultaneously maintaining the totalillumination upon the mosaic at a predetermined substantially constantvalue.

8. A television system comprising a cathode ray tube having a mosaicelectrode, means for projecting a light image of an object upon themosaic electrode, and optical means including a flooding light beam forsimultaneously irradiating the entire mosaic area with diffused lighthaving constant density of illumination.

9. A television system comprising a cathode ray tube having a mosaicelectrode, means for projecting a light image of an object upon themosaic electrode, and flooding light beam means for simultaneouslysuperimposing upon the mosaic electrode area light of constant intensityand constant density.

10. A television system comprising a cathode ray tube having a mosaicelectrode, means for projecting a light image of an object upon themosaic electrode, flooding light beam means for simultaneouslysuperimposing upon the entire mosaic electrode area light of constantintensity and constant density, and means for regulating the intensityin accordance with the average value of illumination of the light image.

11. A television system comprising a cathode ray tube having a mosaicelectrode, means for projecting a light image of an object upon themosaic electrode, flooding light beam means for simultaneouslysuperimposing upon the entire mosaic electrode area light of constantintensity and constant density, and means for regulating the intensityinversely proportional to the average light value of illumination of thelight image.

12. A television system comprising a cathode ray tube having a mosaicelectrode, means for projecting a ligh image of an object upon themosaic electrode, flooding light beam means for simultaneouslysuperimposing upon the entire mosaic area difiused light of constantdensity, means for scanning the mosaic to produce distorted signalsrepresentative of the illumination of the combined image and diffusedand means for transmitting the produced signals together with signalsfor compensating for the distortion.

RUDOLF URTEL.

